This invention relates to ion implantation of semiconductor wafers in a vacuum chamber and, more particularly, to an assembly for mounting wafers and for measuring an ion beam.
In the fabrication of integrated circuits, a number of processes have been developed which involve the application of charged particle beams onto semiconductor wafers in vacuum. These processes include ion implantation, ion beam mulling and reactive ion etching. In each instance, a beam of ions is generated in a source and is directed with varying degrees of acceleration towards a target. Ion implanation has become a standard technique for introducing impurity dopants into semiconductor wafers.
Automated ion implantation systems typically include an ion source, ion optics, means for deflecting the ion beam and an end station for mounting and exchanging wafers. The end station includes a platen assembly for mounting a semiconductor wafer in the path of the ion beam, a wafer handler for automatic exchange of wafers and means for measuring the ion beam applied to the wafer. Typically, the wafer is clamped at its periphery to a platen which acts as a heat sink for energy imparted to the wafer by the ion beam. The platen is rotated between an ion implantation position in which it is generally perpendicular to the ion beam and one or more wafer exchange positions where the wafers are unclamped and exchanged. In addition, prior art systems usually include a so-called beam setup flag, which is rotated into the beam path in front of the wafer-mounting platen. The beam setup flag includes a Faraday cup and is used to adjust parameters of the ion beam such as current, focus and centering by measuring the beam current. During implanation of wafers, the beam setup flag is rotated out of the beam path.
In prior art systems, the beam setup flag has been a separately-controlled unit mounted upstream of the platen toward the source. This configuration has several disadvantages. The Faraday charge collection system used for measuring target dosage extends from the platen in the direction of the ion source and encloses the beam setup flag. The length of the beam path and of the Faraday system are increased by the presence of the beam setup flag. In addition, the beam setup flag is not in the wafer plane when the beam is being measured. Therefore, forus in the wafer plane cannot be accurately determined. Furthermore, the beam setup flag requires an actuator, a control system and a cooling system to remove heat. The cooling connections and the electrical connections to the Faraday cup must be made through rotary feedthroughs, since the assembly is mounted for rotation. Therefore, complexity and cost are added to the ion implantation system.
It is a general object of the present invention to provide novel ion implanation apparatus.
It is another object of the present invention to provide a novel platen and beam setup flag assembly for an ion beam processing system.
It is yet another object of the present invention to provide a platen and beam setup flag angularly displaced for rotation about a common mounting shaft.